This invention relates to a waterbrake cylinder for use in the deceleration of a test sled.
Waterbrakes for test sleds include a braking cylinder which receives a piston secured to the test sled and has an inside diameter corresponding to the diameter of the sled piston. The cylinder is filled with water and is permanently closed with a thin plastic membrane. Prior art cylinders have radial holes drilled in the top portion of the cylinder. The holes are threaded to receive either small orifices or plugs so that the area for discharge of water may be varied.
When the front of the sled piston engages the waterbrake, the piston breaks the plastic membrane and enters the waterbrake cylinder. The piston increases the water pressure in the cylinder which causes the sled to decelerate and causes water to discharge through the orifices. As the piston passes each orifice opening, the orifice becomes closed off, leaving only the remaining downstream orifices for the escape of water. This provides, in effect, an orifice area which is a function of the deceleration distance. The operation of the brake depends on the transfer of energy from the moving sled to moving water.
Waterbrake cylinders having a spiral pattern of openings drilled in the cylinder have been proposed.